Table 1. Species number, physical size, and genome size of microbes. All data in this table represent estimates only. The C-value is a rough estimate of genome size and is based on the amount of DNA in picograms (pg) in a haploid nucleus (Gregory 2004). The genome size range of protists is several orders larger than any other group primarily because of the reported genome size of Amoeba dubia. The physical size of most eubacteria fall within a 1–3 µm range, however, the recently discovered giant eubacterium Thiomargarita namibiensus is greater than 750 µm in diameter.
Organism Number of known species Predicted number of species Size range (µm) Genome size range, C-value (pg)
eubacteria 9000 10,000,000 0.1–750 10-3–10-2
archea 300 ? 1–? 10-3–10-2
fungi >74,000 1,500,000 5–5.6 × 109 10-2–1.0
algae >34,000 400,000 1–6 × 107 10-2–10-1
protists >42,000 400,000 2–200 10-2–103
viruses >2000 10,000,000 0.005–0.4 10-6–10-2